we asked for the users' full name when they registered, and had the visibility of the field turned on. Now users have complained that Google caches those realnames and makes them susceptible to searches. For increased privacy, I was trying to set the visibility of the "Full Name" field to false, but in the Admin Control Panel, under "Users & Groups" -> Profile Fields, there are no defined fields to edit. This might have to do with our installation, which still has the occasional hiccup compared to a clean reinstall. Where do I have to go to edit the visibility of the field - which file is the value stored in (I can edit the .php, I did not find where it is saved)?

FUDForum uses a template mechanism... I suggest you create a theme for your site (based on the default) find the .tmpl files that you wish to edit, copy them to your theme, then edit them. Use the "Rebuild all themes" function when you're done.